Flash Tanks : Boiler Room Guides

Flash tanks, also known as flash vessels or separators, are used to separate the vapor and liquid phases of a mixture. These tanks work by rapidly reducing the pressure on a heated liquid mixture, causing some of the liquid to vaporize or “flash” into steam.

The resulting two-phase mixture of steam and liquid is then separated in the tank. The steam is then captured for further use, and the liquid is returned to the system.

One of the key benefits of flash tanks is that it is able to recover flash steam for other uses. In a power plant, they can be used to separate water vapor from flash steam after the steam has passed through the turbine. The recovered steam can then be used for additional low pressure steam applications.

Types Of Flash Tanks

There are several different types of tanks available, each with their own specific advantages and disadvantages. For example, horizontal tanks are typically used for low-pressure applications, while vertical tanks are better suited for high-pressure applications.

These tanks are typically made of metal materials, such as carbon steel, stainless steel, or aluminum. The choice of material depends on the operating conditions of the tank and the intended service life.

The components that make up the flash tank such as the nozzles, flanges, and other attachments also need to be considered. It is important to ensure that these components are compatible with the process and the materials of construction.

Design Pressures

The pressure rating is one of the key design parameters for a flash tank. It is established based on the intended use and operating conditions of the tank.

The ASME Boiler and Pressure Vessel Code sets the standards for pressure ratings. The pressure rating for flash tanks is typically in the range of 150 psi to 350 psi. However, this can vary depending on the specific application, the size and material of the tank, and the safety factors used in the design.

Tank Sizing

Sizing a flash tank involves determining the flow rate of the liquid mixture entering the tank. A larger flow rate requires a larger tank to accommodate the increased volume of liquid and steam. The pressure drop across the flash tank must be considered when sizing the tank. The operating pressure, temperature and space must also be considered.

Originally published at https://www.rasmech.com on January 20, 2023.